Dissecting All Things Biological

Loggerhead turtle trapped in fishing net, unable to get to the surface to breathe. Source: https://www.nationalgeographic.com/magazine/2018/06/plastic-planet-animals-wildlife-impact-waste-pollution/

The dangers of microplastics within the terrestrial world made the headlines last week when it was discovered that microplastics pass through each stage of a mosquito’s life and consequently, as birds find them to be something of a delicacy, end up in our feathered friends. However, this week it’s the impact of microplastics on the marine world that’s making waves. A group of researchers from the University of Exeter have uncovered the devastating effects of microplastics on both loggerhead and green turtles in the Mediterranean.

Microplastics, tiny pieces of plastic less than 5mm, find their way into the world’s oceans both directly, through industrial spills and runoff, and indirectly by the breakdown of macroplastics into microplastics by abrasive actions such as weathering.

Unfortunately, this plastic is now everywhere, accounting for 86% of all human-caused marine debris worldwide. Whilst we are familiar with some of the impacts of macroplastics on marine life, such as six-pack rings preventing the normal growth of an animal or carrier bags resulting in suffocation, the hidden threats of microplastics are only just beginning to surface.

The study conducted took place at loggerhead and green turtle nesting sites on beaches across Cyprus. Beaches which were far from industry and therefore not subject to the primary source of microplastics. Nonetheless they were found across all 17 of the sites sampled.

The nesting sites of these turtles can be found around 60cm deep in the sand, and no surprise, microplastics had made it down this far. The plastics become incorporated into the sand through alterations in the beach caused by a variety of factors including wave action and weather patterns which continually disrupt and move the sand.

Turtles have an interesting feature of reproduction in that the sex of their offspring is determined by the temperature the eggs are incubated at. Microplastics have the potential to alter this temperature, thus creating a problem. If they alter the temperature too much a certain way, then the ratio of males to females could become skewed in favour of one or the other. Too many or too few of each will make future reproduction of the species problematic.

It is not yet known the extent to which microplastics impact temperature as studies have shown it to both increase and decrease nest site temperatures. However, it is known for certain that there is at least an effect.

Perhaps the most troubling consequence of microplastics on turtle development is the alteration of water availability which marine turtles rely on heavily during development. Microplastics reduce the availability of water to the nesting sites by increasing the permeability of the sand. Nests then fail due to desiccation.

It has been made clear that the effects of plastic go well beyond death to an animal through entanglement or ingestion. Turtles provide just one example of the disastrous effects of plastic. Unfortunately, due to its abundance and mobility it has the potential to infiltrate and interact with all ecosystems and species globally, giving me reason enough to conclude that it is one of the greatest threats to biodiversity today.

A note from the author:

The more I come to learn about the impacts of plastic on the world we were so lucky to be provided, the more I am reminded than not that we are not worthy of it. I challenge you all to try and cut out one unnecessary piece of plastic from your life this week. Whether you switch from hand soap from a plastic bottle to a bar of soap, or a regular toothbrush to one made of bamboo, as Tesco likes to say, every little really does help.